A standard creel has a plurality of stations each provided with a support for a respective yarn package, a respective thread brake that maintains a predetermined minimum tension in the filament between it and the downstream warp beam or the like, and a respective thread clip. These clips are all ganged and are opened simultaneously when the machine is started up and similarly closed simultaneously when the machine is stopped to keep the yarn taut.
It is standard in such arrangements to provide for each yarn supply a respective sensor which detects the tension in the respective yarn and responds when this tension drops below a certain threshold, as when a yarn breaks or runs out. A controller connected to all of the sensors immediately arrests the takeup beam of the warping machine or similar device when any of the tension sensors outputs a low-tension signal. In this manner it is possible to correct the problem, typically by rethreading the broken filament through the respective brake and clip and knotting it to the free end of the package it broke off or to the free end of a new package, and then restart the machine.
As described in German Pat. No. 3,100,880 the thread brake used to control tension during startup of the machine is formed as a pair of parallel and spaced vertical rods extending past each vertical row of yarn supplies. The respective yarns pass between these rods, one of which is movable relative to the other to vary the contact line, that is the length of the piece of filament contacting both rods at one time, and thereby vary drag on the yarn. Such a brake is provided, in the filament travel direction, upstream of the tension sensor, and is set for maximum contact and, therefore, maximum drag at startup to prevent the sensor from responding. Once the yarn is up to speed the drag is normally backed off at the brake since most frictional drag is proportional to speed so that the drag at other points is sufficient to maintain the yarn tension above the response threshold of the low-tension detector. In this system the thread clip, which is independent of the brake, releases the filament as the machine is started up, a release which is not altogether instantaneous to reduce wear to the jaws of the clip.
This system puts considerable stress on the yarn since the tension during startup at least momentarily exceeds the tension necessary to wind it up. In addition the tension varies due to the rapid opening of the respective clip in connection with the slow tension increase as the takeup element gets up to speed and with the speed-related effectiveness of the rod-type brake. In addition the device is expensive to make so it gives satisfactory and uniform results.